Generally, a spring is used for the purpose of shock-absorbing and accumulating energy through elastic force of a steel wire, or for the purpose of assuring of various functions of machine elements using a restoring force occurring after compression.
A coil spring that is prepared by coiling a round wire is the most typical spring shape. The coil spring may be classified into a cold coiled spring and a hot coiled spring depending on the production method.
The cold coiled spring is produced in such a way as to directly coil an OT wire (Oil Tempered Wire) or an IT wire (Induction Treatment Wire) that is previously heat-treated during production of a spring wire without an additional heating operation, and the hot coiled spring is produced in such a way that a wire is cut into a wire piece having a length corresponding to a spread length of a hot coiled spring to be produced, the cut wire is heated to a predetermined temperature and coiled, and the coiled wire is subjected to a heat-treatment to have a desired strength.
FIG. 1 is a view showing a conventional process of producing a cold coiled spring.
For the production of a cold coiled spring, a wire that has been subjected to a predetermined heat treatment is rolled, and the rolled wire is transferred to an apparatus 20 for manufacturing a coil spring by means of a feeding unit 10 composed of a plurality of rolls.
The apparatus 20 produces a cold coiled spring in such a way that the wire supplied through the feeding unit 10 is coiled by means of a plurality of forming rolls 21, and then a rear end of the coiled wire is cut using a cutting unit 30.
Because the cold coiled spring is produced from a wire that is previously heat-treated so as to have a desired strength, the coil spring is expensive due to the increased cost of raw material and it is not easy to produce a coil spring having a large coil diameter.
FIG. 2 is a view showing a conventional process of producing a hot coiled spring.
For the production of a hot coiled spring, a wire is first cut into a wire piece having a length corresponding to a spread length of a hot coiled spring to be produced, the cut wire is heated in a heating unit, and the heated wire is coiled by means of a hot coiling machine 40.
The hot coiling machine 40 produces a coil spring by holding an end of the wire using a mandrel 41 and rotating the mandrel 41. While the coil spring that is produced in this way requires an additional heating unit, price of the coil spring can be decreased because the raw material is inexpensive compared to a cold coiled spring.
However, in order to produce coil springs having different coil diameters or shapes, the coiling machine that uses the mandrel inevitably requires mandrels corresponding to the various coil springs. Consequently, various types of mandrels have to be prepared and a required one among the mandrels has to be selected and used depending on an application, the working efficiency is deteriorated.
Of course, though a wire can be deformed into a coil spring shape by means of a plurality of forming rolls as in the production of cold coiled spring, the process using the forming rolls requires a compulsory transfer of the wire toward the forming rolls by means of a feeding unit. During the transfer of the wire, the plurality of rolls come into contact with the wire thus causing heat loss of the wire. Due to the heat loss, a temperature of the wire introduced into the coiling machine is decreased thus impeding proper forming of the wire.